1. Field of the Invention
This invention relates to a method of filling a liquid droplet ejection head of ink jet system with a function liquid such as ink, or the like; a liquid droplet ejection apparatus; an electrooptic device; a method of manufacturing the electrooptic device; and an electronic apparatus.
2. Description of the Related Art
In a liquid droplet ejection apparatus as represented by an ink jet printer, the following arrangement is conventionally employed. Namely, when a flow passage inside an ink jet head (liquid droplet ejection head) is filled with an ink, a positive pressure is given to an ink tank (function liquid storing part) in which the ink is stored so as to send or feed the ink under pressure (i.e., in a pressurized state) from the ink tank to the ink jet head through a tube (see, e.g., Published Unexamined Japanese Patent Application No. 2000-21157, FIG. 2 and related description).
To the contrary, there is also known one in which, when the ink is filled, the ink jet head is sealed by a cap. By driving a suction pump which is connected to the cap, a negative pressure is given to the flow passage inside the ink jet head and to the tube to thereby feed the ink from the ink tank (see, e.g., Published Unexamined Japanese Patent Application No. 286974/1998, FIG. 5 and related description).
If air bubbles remain or stay in the flow passage inside the ink jet head, the liquid droplet ejection head causes poor ejection from the nozzles. On the other hand, in the liquid droplet ejection apparatus to be used in forming various film-forming parts of a color filter, organic electroluminescence (EL) device, or the like, there are cases in which function liquids such as special inks from which air bubbles cannot be completely removed are used.
In the conventional filling method using the negative pressure, there is a possibility that air bubbles are generated in the tube and in the flow passage inside the liquid droplet ejection head, depending on the characteristics of the function liquid, due to the gases held in solution inside the function liquid. In such a case, in order to remove the residual air bubbles, the necessity arises of discharging the air bubbles together with the function liquid droplet out of the flow passage inside the head through the nozzle by repeating the suction several times. This results in a wasteful consumption of expensive function liquids.
On the other hand, in the conventional filling method using the positive pressure, the air bubbles will not be generated in the tube and in the flow passage inside the head at the time of filling. However, there is a problem in that, if air bubbles stay in the corner portion of the flow passage inside the head (i.e., inside the main body portion of the head) due to the surface tension of the function liquid, these air bubbles cannot easily be discharged toward the nozzle by the liquid feeding under positive pressure.